THE EFFECT OF CLAY SLIMES ON COAL FLOTATION .1. THE NATURE OF THE CLAY

Kaolinite and illite, which do not significantly depress coal flotation, contaminate the floated clean coal largely by carry-over with the froth, although electrostatic attachment to the coal contributes in a lesser way to the ash content of the froth. Bentonite depresses all but the most hydrophobic coals by armour coating of the bubbles, preventing coarse particle attachment, and increasing slime coatings, all because of its high surface area, charged sites, and ion exchange capacity. Common clay dispersants depress coal flotation. Fuel oil improves coal recovery in the presence of clay slimes, but the ash and pyrite content of the floated coal also increases.